Method of manufacturing a display device

ABSTRACT

ICs ( 20 ) are nearly separated from the semiconductor substrate ( 10 ) on/in which they are formed. Subsequently, the substrate is positioned upside down on a substrate (carrier) ( 3 ) which is provided with glue ( 21 ) at the location of a crystal. After attachment of the crystal to the carrier, the semiconductor substrate is removed and the crystal remains attached to the carrier e.g. at the crossing of rows and columns. The separate crystals may contain TFTs (simple AM addressing) but also more complicated electronics (address of pixel in memory+identification).

The invention relates to a method of manufacturing a display device, inwhich a substrate is provided with groups of at least one pixel and aconductor pattern, and in which a semiconductor device for supplyingdrive voltages to the pixel is fixed to the substrate.

Examples of such active matrix display devices are the TFT-LCDs orAM-LCDs which are used in laptop computers and in organizers, but theyalso find an increasingly wider application in GSM telephones. Insteadof LCDs, for example, (polymer) LED display devices can be used.

More generally, the invention relates to a method of manufacturing anelectronic device, in which at least a substrate is provided withfunctional groups comprising at least a switching element, and in whicha semiconductor device for supplying drive voltages to the switchingelement is fixed to the substrate.

The article “Flexible Displays with Fully Integrated Electronics”, SIDInt. Display Conf., September 2000, pp. 415 to 418, describes a processin which specifically formed semiconductor devices in a liquidsuspension are passed across a substrate and reach correspondinglyformed “apertures” or indentations in the substrate. The semiconductordevices are ICs which are manufactured by means of standard techniques.After the ICs have been provided, connections with pixels areestablished.

A problem occurring in this case is the fact that, for providing theICs, considerable tolerances are to be taken into account. Not only mustthe semiconductor devices (ICs) glide, as it were, into the indentationsbut they also have a certain thickness (approximately 50 micrometers).Dependent on variations of thickness, certainly when not all ICs comefrom one and the same wafer, and variations on the surface of thesubstrate in the depth of the “apertures” or indentations, a variationwill occur in the thickness of the electro-optical layer provided on thesubstrate, which thickness may amount to several micrometers. Notablywhen thickness-sensitive effects such as, for example, the (S)TN effectare used, this leads to unwanted discoloration and non-uniform switchingbehavior.

Inaccuracies during placement of the ICs must also be taken intoaccount. When an IC “glides into the indentations”, it may find itsultimate destination at an arbitrary location within this indentation.Consequently, the indentations occupy a much larger space than thesemiconductor devices (ICs), which, notably in transparent displaydevices, is at the expense of the aperture. To be able to satisfactorilycontact the ICs in the case of this inaccurate placement, these ICs mustbe provided with large contact surfaces, which is at the expense of ICsurface area and renders the technology shown very expensive.

A further problem is the variation of the thickness of the semiconductordevices (ICs), related to the depth variation of the indentations sothat local thickness variations occur in the ultimate surface area (thecommon surface area of the substrate). Conductor tracks extending in thedevice shown across the embedded semiconductor devices (ICs), therebyrun a great risk of breakage.

To this end, a semiconductor substrate according to the invention isprovided with a plurality of semiconductor devices whose surfaces haveelectric connection contacts, the semiconductor devices being mutuallyseparated in a surface region of the semiconductor substrate and theelectric connection contacts being coupled to the conductor pattern (inan electrically conducting manner) whereafter the semiconductor devicesare separated from the semiconductor substrate.

Since the semiconductor devices (ICs) are similarly situated withrespect to each other as on the semiconductor substrate during theirfixation to the substrate, the ICs are provided at a very accuratepitch. This may be a constant pitch in one direction, such as inmatrix-shaped configurations of the pixels. The pitch may alternativelybe variable.

Moreover, due to this method of fixation, only parts of the surface areaof the semiconductor substrate in which the active elements are realizedcan be provided on the substrate of the display device. Since theseparts have a negligible thickness (less than 1 micrometer), saidthickness-sensitive effects do not occur. Even the presence of a spacerat the location of an IC does not have any influence or hardly has anyinfluence on the effective thickness of the liquid layer and hence onthe operation of the display device, certainly when spacers with anelastic envelope are chosen.

A further advantage is that the ICs can now comprise drive electronicsat the location of the pixels. This provides great freedom of design.

The semiconductor devices are separated, for example, by means of anetching treatment in a surface area of the semiconductor substrate. Inan alternative method, the semiconductor devices are provided in asemiconductor layer on an insulating layer (SOI technology) andseparated by means of an etching treatment in this semiconductor layerhaving a thickness of typically 0.2 micrometer. The result is that thesesemiconductor devices in the finished display device have a negligiblethickness (less than 1 micrometer) as compared with the effectivethickness of the liquid layer, so that said thickness-sensitive effectsdo not occur, not even in the presence of a spacer at the location of anIC. Moreover, the ICs are now placed with great accuracy and withouttaking extra precautions. The contact surfaces may now be considerablysmaller, which occupies less IC surface.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 is a diagrammatic cross-section of a part of a display deviceaccording to the invention,

FIG. 2 shows diagrammatically a flow chart of the method,

FIGS. 3 and 4 show diagrammatically steps during the manufacture of thedisplay device of FIG. 1,

FIGS. 5 and 6 show diagrammatically the semiconductor substrate and thesubstrate of the display device during manufacture of the display deviceof FIG. 1, while

FIG. 7 is an electrical equivalent of a possible embodiment of a displaydevice according to the invention, and

FIG. 8 shows an electron-microscopic image of the semiconductorsubstrate for fixation of the display device to the substrate.

The Figures are diagrammatic and not drawn to scale. Correspondingelements are generally denoted by the same reference numerals.

FIG. 1 is a diagrammatic cross-section of a part of a light-modulatingcell 1 with a liquid crystal material 2 which is present between twosubstrates 3, 4 of, for example, glass or synthetic material, providedwith (ITO or metal) electrodes 5, 6. Together with an intermediateelectro-optical layer, parts of the electrode patterns define pixels. Ifnecessary, the display device comprises orientation layers (not shown)which orient the liquid crystal material on the inner walls of thesubstrates. The liquid crystal material may be a (twisted) nematicmaterial having, for example, a positive optical anisotropy and apositive dielectric anisotropy, but may also make use of the STN effect,a bistable effect, a chiral nematic effect, or the PDLC effect. Thesubstrates 3, 4 are customarily spaced apart by spacers 7, while thecell is sealed with a sealing rim 8 which is customarily provided with afilling aperture. A typical thickness of the layer of liquid crystalmaterial 2 is, for example, 5 micrometers. The electrodes 5, 5′ have atypical thickness of 0.2 micrometer, while also the thickness of thesemiconductor devices (ICs) 20 is about 0.2 micrometer in this example.In FIG. 1, a spacer 7 is shown at the location of an electrode 5′ and IC20. The overall thickness of electrode and IC 20 is substantiallynegligible as compared with the thickness of the layer of liquid crystalmaterial 2. The presence of the spacer 7 does not have any influence, orhardly has any influence, on the opto-electrical properties of thedisplay device, notably when spacers with a hard core 8 and an elasticenvelope 9 having a thickness of about 0.2 micrometer are chosen.

For manufacturing the semiconductor devices (transistors or ICs) 20, useis made of conventional techniques. The starting material is asemiconductor wafer 10 (see FIG. 2, step I^(a), FIG. 3), preferablysilicon, with a p-type substrate 11 on which an n-type epitaxial layer15 having a weak doping (10¹⁴ atoms/cm³) is grown. Prior to this step, amore heavily doped n-type layer 13 (doping about 10¹⁷ atoms/cm³) isprovided by means of epitaxial growth or diffusion. Further processsteps (implantation, diffusion, etc.) realize transistors, electroniccircuits or other functional units in the epitaxial layer 15. Aftercompletion, the surface in the example of FIG. 3A is coated with aninsulating layer such as silicon oxide. Contact metallizations 17 areprovided via contact apertures in the insulating layer by means oftechniques which are customary in the semiconductor technology. Ann-type region 14 (doping about 10¹⁷ atoms/cm³) is provided between thetransistors, electronic circuits (ICs) or other functional units,likewise by masked doping (before or after providing the insulatinglayer 16).

FIG. 3B shows a variant of FIG. 3A, in which the transistors, electroniccircuits or other functional units are realized in the SOI technology inwhich the thin surface area 15 is embedded in insulating layer 19. Inthe example of FIG. 3B, the contact metallizations 17 are directlyprovided on contact regions of the transistors of the semiconductordevices.

Subsequently, the n-type regions 14 are subjected via a mask to anetching treatment with HF (under the influence of an electric field). Inthis treatment, the heavily doped n-type region 14 is isotropicallyetched, as well as the underlying n-type epitaxial layer 13. The weaklydoped n-type epitaxial layer 15 is, however, etched anisotropically sothat, after a given period, only a small region 25 remains in this layer(see FIG. 2, step I^(b) FIG. 3).

The transistors, electronic circuits (ICs) or other functional unitsare, however, still at their originally defined position. A regularpattern of such units will generally be manufactured at a fixed pitch.

Prior to, simultaneously with or after this treatment, substrates 3 ofthe display device are provided with metallization patterns which (alsoat defined positions) will comprise one or more electrodes 5′ (FIG. 2,steps II^(a), II^(b)). In this example, the parts 5′ of themetallization patterns on the substrate 3 are ordered similarly (thesame pitch in different directions) as the electronic circuits (ICs) 20in the semiconductor wafer 10.

In a subsequent step, the semiconductor wafer 10 is turned upside down,in which the metallization patterns 5′ on the substrate 3 are accuratelyaligned with respect to the electronic circuits (ICs) 20 in thesemiconductor wafer 10 (FIG. 4), whereafter electrical contact isrealized between metallization patterns 5′ and the contactmetallizations 17. To this end, use is made of, for example, aconducting glue 21 or anisotropically conducting contacts on theelectrodes 5′. The electronic circuits (ICs) 20 are detached from thesemiconductor wafer 10 by means of vibration or by a different method.The substrate 3 is then obtained which is provided with pictureelectrodes 5 and ICs 20 which are very accurately aligned both withrespect to the picture electrodes 5 and with respect to each other (stepIII in FIG. 2). Moreover, the reduction of aperture is exclusivelydetermined by the dimension of the ICs (or transistors).

Also when using SOI technology, a first separation between the variouselectronic circuits (ICs) 20 can be made by means of a HF etchingtreatment or other methods which are conventional in the semiconductortechnology, which ICs are subsequently detached from the substrate alsoby means of vibration or by means of another method.

Not all ICs (transistors) of the substrate 10 are detached from thesubstrate during this step, because the pitch p₀ of the metallizationpatterns 5′ is usually much larger than the pitch p₁ and pitch p₂ of theICs 20. This will be further explained with reference to FIG. 5. If thesubstrate 3 has a size of the order of (or smaller than) the regionindicated by the block 22 of detachable ICs, only the ICs 23 (black ICsin FIG. 5) are detached and provided on the substrate.

If the substrate 3 is larger than the diagrammatically shown block 22 ofdetachable ICs, the ICs 23 (black ICs in FIG. 5) are first detached andprovided on the part 26 on the substrate 10 (see FIG. 6). Subsequentlythe adjacent ICs 24 (see FIG. 5) are detached and provided on the part27 of the substrate 10. Similarly, ICs 20 are provided on the parts 28,29.

The display device 1 is subsequently completed in a customary manner, ifnecessary, by providing orientation layers which orient the liquidcrystal material on the inner walls of the substrate. Spacers 7 arecustomarily provided between the substrates 3, 5, as well as a sealingrim 8 which is customarily provided with a filling aperture, whereafterthe device is filled with LC material in this example (step IV in FIG.2).

Since the semiconductor devices (ICs) 20 are made in advance, moreextensive electronic functions can be realized therein than in theconventional polysilicon technology. Notably when using monocrystallinesilicon, it is possible to realize functions with which a different typeof architecture of the display device can be made possible than with theconventional matrix structure. Such a device 30 is shown in FIG. 7,which is a device having a bus structure. The ICs (semiconductordevices) 20 are connected to a supply voltage via connection lines 31,32 (in this example, line 31 is connected to earth), while the lines 33,34 supply information and, for example, a clock signal. Since, asdescribed above, the location of an IC to be provided is known inadvance, this may be provided first (during IC processing or via e-PROMtechniques), for example, with an address register and one or more dataregisters. For certain ICs (and associated (groups) of pixels 35), theaddress is recognized by the ICs and picture information is stored,whereafter it is applied to the pixels 35, dependent on commands to bealso supplied through the lines 33, 34.

FIG. 8 is an electron-microscopical image of the semiconductor substratefor fixation to the substrate (FIG. 2, step I^(b)).

The protective scope of the invention is not limited to the embodimentdescribed. As stated in the opening paragraph, the pixels may also beformed by (polymer) LEDs which may be provided separately or as oneassembly, while the invention is also applicable to other displaydevices, for example, plasma displays, foil displays and display devicesbased on field emission, electro-optical or electromechanical effects(switchable mirrors). Where the examples state a pitch in an orthogonalsystem of co-ordinates, the localization may also take place in a radialsystem of co-ordinates or in a tree structure (fractal structure). Asalready stated, the pitch may also be variable. This provides thepossibility of manufacturing, for example, circular or elliptic displaydevices.

The examples stated the direct electric contact of the ICs onmetallization patterns 5′ that were already present. Since the detachedICs have a small thickness, they may also be provided directly on thesubstrate 3, in which method apertures which are metallized are etchedthrough the layers 15 by means of an etching method. The contactmetallizations then extend across the ICs and make contact (for example,via contact apertures in an insulating layer) with through-metallizedconnections to the contact metallizations 17.

Said contacts do not need to be electrically conducting contacts. Ingiven applications, it may be useful to provide a capacitive couplingbetween the contact metallizations 17 and the metallization patterns 5′,for example, by providing one or both with a thin insulating layer.

As also stated in the opening paragraph, the method is not limited todisplay devices. The invention is notably applicable to electronicdevices (sensors) in which the substrate is provided with functionalgroups.

Alternatively, as stated, flexible substrates (synthetic material) maybe used (wearable displays, wearable electronics).

The invention resides in each and every novel characteristic feature andeach and every combination of characteristic features. Referencenumerals in the claims do not limit their protective scope. Use of theverb “to comprise” and its conjugations does not exclude the presence ofelements other than those stated in the claims. Use of the article “a”or “an” preceding an element does not exclude the presence of aplurality of such elements.

What is claimed is:
 1. A method of manufacturing a display device, inwhich a substrate is provided with groups of at least one pixel and aconductor pattern and in which a semiconductor device for supplyingdrive voltages to the pixel is fixed to the substrate, the methodcomprising the steps of providing a semiconductor substrate with aplurality of semiconductor devices having electric connection contactson their surfaces, mutually separating the semiconductor devices in asurface region of the semiconductor substrate, coupling the electricconnection contacts to the conductor pattern, and subsequentlyseparating the semiconductor devices from the semiconductor substrate.2. A method as claimed in claim 1, wherein at least a part of theelectric connection contacts is connected to the conductor pattern in anelectrically conducting manner.
 3. A method as claimed in claim 1,wherein the semiconductor devices have the same pitch as the groups ofpixels in at least one dimension.
 4. A method as claimed in claim 1,wherein a semiconductor device is associated with a plurality of pixels.5. A method as claimed in claim 4, wherein the semiconductor devicecomprises device electronics for the pixels.
 6. A method as claimed inclaim 1, wherein the semiconductor devices are separated by means of anetching treatment in a surface region of the semiconductor substrate. 7.A method as claimed in claim 1, wherein the semiconductor devices areprovided in a semiconductor layer on an insulating layer and areseparated by means of an etching treatment.
 8. A method as claimed inclaim 1, wherein the substrate is flexible.
 9. A method of manufacturingan electronic device, in which at least a substrate is provided withfunctional groups comprising at least a switching element, and in whicha semiconductor device for supplying drive voltages to the switchingelement is fixed to the substrate, the method comprising the steps ofproviding the substrate with a conductor pattern, providing asemiconductor substrate with a plurality of semiconductor devices havingelectric connection contacts on their surfaces, mutually separating thesemiconductor devices in a surface region of the semiconductorsubstrate, coupling the electric connection contacts to the conductorpattern, and subsequently separating the semiconductor devices from thesemiconductor substrate.
 10. A method as claimed in claim 9, wherein atleast a part of the electric connection contacts is connected to theconductor pattern in an electrically conducting manner.
 11. A method asclaimed in claim 9, wherein the semiconductor devices have the samepitch as the functional groups in at least one dimension.